Hooked battery cables on backwards has not started since

key ain't got nothing to do with it,if it was working before battery cables were hooked up backwards...you won't do that but "once" in a lifetime,after you get this paid for,you will never forget this or do it again! That's Sulfuric acid inside the battery.you do not EVER want a car battery to blow up and get on your skin,in your eyes and last,not even on your clothes! Yeah,you can probably fix your vehicle,buy new clothes,but the EYES is a different ending!!